Carmarthen West and South Pembrokeshire (Welsh: Gorllewin Caerfyrddin a De Sir Benfro) is a constituency of the Senedd.

The other four Dyfed constituencies were Carmarthen East and Dinefwr, Ceredigion, Llanelli and Preseli Pembrokeshire.

The constituency includes the whole of 22 Carmarthenshire communities (Abernant; Bronwydd; Carmarthen; Cilymaenllwyd; Cynwyl Elfed; Eglwyscummin; Henllanfallteg; Laugharne Township; Llanboidy; Llanddowror; Llangain; Llangynin; Llangynog; Llanpumsaint; Llansteffan; Llanwinio; Meidrim; Newchurch and Merthyr; Pendine; St Clears; Trelech; Whitland), the whole of 24 Pembrokeshire communities (Amroth; Angle; Carew; Cosheston; East Williamston; Hundleton; Jeffreyston; Kilgetty/Begelly; Lampeter Velfrey; Lamphey; Llanddewi Velfrey; Llawhaden; Manorbier; Martletwy; Narberth; Pembroke; Pembroke Dock; Penally; St Florence; St Mary Out Liberty; Saundersfoot; Stackpole and Castlemartin; Templeton; and Tenby), also the eastern part of the Pembrokeshire community of Uzmaston, Boulston and Slebech.

The other four Dyfed constituencies are, again, Carmarthen East and Dinefwr, Ceredigion, Llanelli and Preseli Pembrokeshire, all within the Mid and West Wales electoral region.

For Westminster purposes, the same new constituency boundaries became effective for the 2010 United Kingdom general election.